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Computer Graphics- SCC 342 Chapter 2: Computer Graphics Hardware. Dr. Doaa Hegazy. Overview of a graphics system. 2.1 Video Display Devices. Cathode-ray-tube (CRT). 2.1 Video Display Devices. CRT basics: The screen output is stored in the frame buffer and

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dr doaa hegazy

Computer Graphics- SCC 342

Chapter 2: Computer Graphics Hardware

Dr. Doaa Hegazy

2 1 video display devices
2.1 Video Display Devices
  • Cathode-ray-tube (CRT)
slide4

2.1 Video Display Devices

CRT basics:

  • The screen output is stored in the frame buffer and

is converted into voltages across the reflection plates

via a digital-to-analog converter (DAG)

  • Light is emitted when electrons hit phosphor
  • But light output from the phosphor decays

exponentially with time, typically in 10 – 60

microseconds

– Thus the screen needs to be redrawn or refreshed

– Refresh rate is typically 60 Hz to avoid flicker (“twinkling”)

– Flicker: when the eye can no longer integrate individual light pulses from a point on screen, e.g., due to low refresh rate

slide5

2.1 Video Display Devices

Shadow-mask color CRTs

  • Three different colored phosphors (R, G, B)
  • dots are arranged in very small groups (triads) on coating

We see a mixture of three

colors

Three electron guns (R, G,

B) emit electron beams in a

controlled fashion so that

only phosphors of the

proper colors are excited

2 1 video display devices1
2.1 Video Display Devices
  • Raster – Scan Display
2 1 video display devices2
2.1 Video Display Devices

The Frame Buffer

  • Stores per-pixel information

– Depth of a frame buffer: number of bits per pixel

– E.g. for color representation, 1 bit => 2 colors,

8 bits => 256 colors,

24 bits => true color (16 million colors)

  • Color buffer is only one of many buffers, other

information, e.g., depth, can also be used

  • Implemented with special type of memory in

standard PCs or on a graphics card for fast

redisplay

  • Part of standard memory in earlier systems
2 1 video display devices3
2.1 Video Display Devices

Raster-scan basics:

  • The screen is a rectangular array

of picture elements, or pixels

  • Resolution: determines the

details you can see

number of pixels in an image,

  • e.g.,

1024×768, 1280x1024, 1366 x 768, etc.

  • also in ppi or dpi – pixel or dot per inch
slide9

2.1 Video Display Devices

Raster-Scan Pattern:

  • Horizontal scan rate: # scan lines per second
  • Interlaced (TV) vs. non-interlaced displays
2 1 video display devices4
2.1 Video Display Devices

Random-Scan Display

  • Also called Vector-scan display
  • Pictures are generated as line drawings
2 1 video display devices5
2.1 Video Display Devices

Flat-Panel Display

  • A class of video devices that have reduced volume, weight and power
  • Two categories:
    • Emissive displays: convert electrical energy to light (e.g. Plasma panels and Light-emitting diode (LED)
    • Nonemissivedisplays: use optical effect to convert light from a certain source into graphics patterns (e.g. Liquid-crystal display (LCD)
2 2 raster scan systems
2.2 Raster-Scan Systems
  • Simple raster-graphics system
  • Video controller (display processor) controls operations of display device.
2 2 raster scan systems1
2.2 Raster-Scan Systems
  • Raster system with fixed portion of main memory reserved for the frame buffer.
2 2 raster scan systems2
2.2 Raster-Scan Systems
  • Video controller
2 2 raster scan systems3
2.2 Raster-Scan Systems
  • Raster – scan display processor

- Digitizes picture definition into a set of pixel values for storage in the frame buffer (scan conversion).

2 2 raster scan systems4
2.2 Raster-Scan Systems
  • Additional functions for Raster – scan display processor

- generating line styles

- display color areas

- transformations

- interface with interactive devices.

slide17

2.4 Input Devices

  • Input devices include
  • Pointing/locator devices:
  • indicate location on screen

– Mouse/trackball/spaceball

– Data tablet

– Joystick

– Touch pad and touch screen

  • Keyboard device: send character input
  • Choice devices: mouse buttons, function keys